NextJS example

[YousefED]

Quite some questions about integrating with NextJS. Let's add this to the docs!

I also made a demo here; https://github.com/YousefED/blocknote-examples-nextjs

This will become even more important now that the official React docs recommend getting create-next-app above create-react-app! See https://react.dev/learn/start-a-new-react-project

[Ianduha13]

The url is fallen, do you have another one to show us the example?

[YousefED]

New docs at #274